The present invention is directed to compounds of formula I 
and enantiomers, diastereomers and pharmaceutically acceptable salts thereof wherein
R is alkyl;
R1 is hydrogen or alkyl;
X is NR2 or CHNR2R3;
R2 and R3 are each independently hydrogen, alkyl, substituted alkyl, cycloalkyl or substituted cycloalkyl; and
n is 0, 1, 2 or 3.
The compounds of formula I are particularly useful as potent, protein kinase inhibitors and are useful in the treatment of proliferative diseases, for example, cancer, inflammation and arthritis. They may also be useful in the treatment of Alzheimer""s disease, chemotherapy-induced alopecia, and cardiovascular disease.
The present invention provides for compounds of formula I, pharmaceutical compositions employing such compounds, and for methods of using such compounds.
Listed below are definitions of various terms used to describe the compounds of the instant invention. These definitions apply to the terms as they are used throughout the specification (unless they are otherwise limited in specific instances) either individually or as part of a larger group.
The term xe2x80x9calkylxe2x80x9d or xe2x80x9calkxe2x80x9d refers to a monovalent alkane (hydrocarbon) derived radical containing from 1 to 12, preferably 1 to 6, and more preferably 1 to 4, carbon atoms unless otherwise defined. An alkyl group is an optionally substituted straight, branched or cyclic saturated hydrocarbon group. When substituted, alkyl groups may be substituted with up to four substituent groups, R4 as defined, at any available point of attachment. When the alkyl group is said to be substituted with an alkyl group, this is used interchangeably with xe2x80x9cbranched alkyl groupxe2x80x9d. Exemplary unsubstituted such groups include methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, isobutyl, pentyl, hexyl, isohexyl, heptyl, 4,4-dimethylpentyl, octyl, 2,2,4-trimethylpentyl, nonyl, decyl, undecyl, dodecyl, and the like. Exemplary substituents may include, but are not limited to, one or more of the following groups: halo (such as F, Cl, Br or I), haloalkyl (such as CCl3 or CF3), alkoxy, alkylthio, hydroxy, carboxy, alkylcarbonyl, alkyloxycarbonyl, alkylcarbonyloxy, amino, carbamoyl, urea, amidinyl, or thiol.
Cycloalkyl is a specie of alkyl containing from 3 to 15 carbon atoms, without alternating or resonating double bonds between carbon atoms. It may contain from 1 to 4 rings. Exemplary unsubstituted such groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc. Exemplary substituents include one or more of the following groups: halogen, alkyl, alkoxy, alkyl hydroxy, amino, nitro, cyano, thiol and/or alkylthio.
The terms xe2x80x9calkoxyxe2x80x9d or xe2x80x9calkylthioxe2x80x9d, as used herein, denote an alkyl group as described above bonded through an oxygen linkage (xe2x80x94Oxe2x80x94) or a sulfur linkage (xe2x80x94Sxe2x80x94), respectively.
The term xe2x80x9calkyloxycarbonylxe2x80x9d, as used herein, denotes an alkoxy group bonded through a carbonyl group. An alkoxycarbonyl radical is represented by the formula: xe2x80x94C(O)OR5, where the R5 group is a straight or branched C1-6 alkyl group.
The term xe2x80x9calkylcarbonylxe2x80x9d refers to an alkyl group bonded through a carbonyl group.
The term xe2x80x9calkylcarbonyloxyxe2x80x9d, as used herein, denotes an alkylcarbonyl group which is bonded through an oxygen linkage.
Pharmaceutically acceptable salts of compounds of formula I which are suitable for use in the methods and compositions of the present invention include, but are not limited to, salts formed with a variety of organic and inorganic acids such as hydrogen chloride, hydroxymethane sulfonic acid, hydrogen bromide, hydrogen iodide, methanesulfonic acid, sulfuric acid, acetic acid, trifluoroacetic acid, maleic acid, fumaric acid, benzenesulfonic acid, toluenesulfonic acid and various others, e.g., nitrates, phosphates, borates, tartrates, citrates, succinates, benzoates, ascorbates, salicylates, and the like. These salts include racemic forms as well as enantiomers, and diastereomers (such as, for example, D-tartrate and L-tartrate salts). In addition, pharmaceutically acceptable salts of compounds of formula I may be formed with alkali metals such as sodium, potassium and lithium; alkaline earth metals such as calcium and magnesium; organic bases such as dicyclohexylamine, tributylamine, and pyridines, and the like; and amino acids such as arginine, lysine and the like.
All stereoisomers of the compounds of the instant invention are contemplated, either in admixture or in pure or substantially pure form. The definition of the compounds according to the invention embraces all possible stereoisomers and their mixtures. It very particularly embraces the racemic forms and the isolated optical isomers having the specified activity. The racemic forms can be resolved by physical methods, such as, for example, fractional crystallization, separation or crystallization of diastereomeric derivatives or separation by chiral column chromatography. The individual optical isomers can be obtained from the racemates by conventional methods, such as, for example, salt formation with an optically active acid followed by crystallization.
All configurational isomers of compounds of the present invention are contemplated, either in admixture or in pure or substantially pure form. The definition of compounds of the present invention very particularly embraces both cis and trans isomers of cycloalkyl rings.
In the context of the present invention, the definition of compounds of the present invention includes the free base, enantiomers, diastereomers as well as pharmaceutically acceptable salts. Examples of such pharmaceutically acceptable salts include, but are not limited to, hydrochloride, dihydrochloride, sulfate, trifluoroacetate, mixture of trifluoroacetate and hydrochloride, tartrate, fumarate, succinate, maleate, citrate, methanesulfonate, bromate and iodate salts. Also included are salts formed with other organic and inorganic acids such as hydroxymethane sulfonic acid, acetic acid, benzenesulfonic acid, toluenesulfonic acid and various others, e.g., nitrates, phosphates, borates, benzoates, ascorbates, salicylates, and the like. These salts include racemic forms as well as enantiomers and diastereomers (such as, for example, D-tartrate and L-tartrate salts). In addition, pharmaceutically acceptable salts of the formula I compounds may be formed with alkali metals such as sodium, potassium and lithium; alkaline earth metals such as calcium and magnesium; organic bases such as dicyclohexylamine, tributylamine, and pyridines, and the like; and amino acids such as arginine, lysine and the like.
It should be understood that solvates (e.g. hydrates) of the compounds of formula I are also within the scope of the present invention. Methods of solvation are generally known in the art. Accordingly, the compounds of the instant invention may be in the free or hydrate form, and may be obtained by methods exemplified by the following schemes.
Compounds of formula I may generally be prepared, as shown in Scheme 1, by reacting an amine of formula II with a carboxylic acid of formula III in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and a base. 
Formula I compounds wherein X is NR2 and R2 is hydrogen may be prepared, as shown in Scheme 2, by reacting an amine of formula II with a carboxylic acid of formula IV in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and a base to form an N-protected compound of formula V, and deprotecting the formula V compound with acid. 
Compounds of formula I wherein X is NR2 and R2 is 2,3-dihydroxypropyl may be prepared, as shown in Scheme 3, by reacting a compound of formula I wherein X is NR2 and R2 is hydrogen with glyceraldehyde in the presence of a reducing agent such as sodium triacetoxyborohydride and an alcohol such as methanol. 
Formula I compounds wherein X is NR2 and R2 is 2-hydroxyethyl may be prepared, as shown in Scheme 4, by reacting a compound of formula I wherein X is NR2 and R2 is hydrogen with a 2-(bromoethoxy)trialkylsilane of formula VI to form an intermediate compound of formula VII, and deprotecting the formula VI compound with an acid such as hydrogen fluoride. 
Starting amines of formula II may be prepared as shown in Scheme 5. An alpha-bromoketone of formula VIII may be reacted with sodium azide in a solvent such as dimethylformamide to provide the azido ketone derivative LX, which is reduced by a reducing agent such as hydrogen in the presence of palladium on carbon catalyst, or triphenylphosphine to provide the amino ketone X. Compound X may alternatively be prepared by reaction of the alpha-bromoketone of formula VIII with hexamethylenetetramine in a solvent such as acetone to give the compound of formula XI, which is hydrolyzed by an acidic medium such as hydrochloric acid in ethanol. Compounds of formula X may be acylated by an agent such as 2-chloroacetyl chloride to provide amides of formula XII. The formula X amides are cyclized to 2-chloromethyl oxazoles of formula XIII using a dehydrating agent such as phosphorous oxychloride in toluene. Reaction of the chloromethyl oxazoles of formula XIII with thiourea in a solvent such as ethanol provides the thiourea derivatives XIV, which may be reacted with 5-bromo-2-aminothiazole in the presence of a base such as potassium hydroxide in alcohol to give formula II amines. Alternatively, reaction of the chloromethyl oxazole derivatives of formula XIII with 5-thiocyano-2-aminothiazole, in the presence of a reducing agent such as sodium borohydride, provides compounds of formula II. 
Preferred compounds of formula I are those wherein:
R is alkyl;
R1 is hydrogen;
X is NR2 or CHNR2R3;
R2 and R3 are each independently hydrogen, alkyl, substituted alkyl or cycloalkyl; and
n is 2.
A first group of more preferred compounds of the present invention are those of formula Ia 
and enantiomers, diastereomers and pharmaceutically acceptable salts thereof wherein R2 is hydrogen, alkyl, substituted alkyl or cycloalkyl.
A second group of more preferred compounds of this invention are those of formula Ib 
and enantiomers, diastereomers and pharmaceutically acceptable salts thereof wherein R2 is hydrogen, alkyl, substituted alkyl or cycloalkyl.
A third group of more preferred compounds of the present invention are those of formula Ic 
and enantiomers, diastereomers and pharmaceutically acceptable salts thereof wherein R2 and R3 are each independently hydrogen, alkyl, substituted alkyl or cycloalkyl.
Formula I compounds particularly useful in the methods of this invention include:
N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-4-piperidinecarboxamide;
(xc2x1)-N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-3-piperidinecarboxamide;
(xc2x1)-1-(2,3-dihydroxypropyl)-N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-4-piperidinecarboxamide;
N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-1-(1-methylethyl)-4-piperidinecarboxamide;
1-cyclopropyl-N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-4-piperidinecarboxamide;
N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-1-(2-hydroxyethyl)-4-piperidinecarboxamide;
(R)-N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-3-piperidinecarboxamide;
(S)-N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-3-piperidinecarboxamide;
cis-4-amino-N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]cyclohexylcarboxamide; and
trans-4-amino-N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]cyclohexylcarboxamide; and
pharmaceutically acceptable salts thereof.
The present invention also includes methods based upon the pharmacological properties of the compounds of the invention. It should be noted that, in the context of the methods of the present invention, the compounds of the invention, or compounds of formula I, refer to the free base, enantiomers, diastereomers as well as pharmaceutically acceptable salts. Examples of such pharmaceutically acceptable salts include, but are not limited to, hydrochloride, dihydrochloride, sulfate, trifluoroacetate, mixture of trifluoroacetate and hydrochloride, tartrate, fumarate, succinate, maleate, citrate, methanesulfonate, bromate and iodate salts. Also included are salts formed with other organic and inorganic acids such as hydroxymethane sulfonic acid, acetic acid, benzenesulfonic acid, toluenesulfonic acid and various others, e.g., nitrates, phosphates, borates, benzoates, ascorbates, salicylates, and the like. These salts include racemic forms as well as enantiomers and diastereomers (such as, for example, D-tartrate and L-tartrate salts). In addition, pharmaceutically acceptable salts of compounds of formula I may be formed with alkali metals such as sodium, potassium and lithium; alkaline earth metals such as calcium and magnesium; organic bases such as dicyclohexylamine, tributylamine, and pyridines, and the like; and amino acids such as arginine, lysine and the like.
The compounds according to the invention have pharmacological properties; in particular, the compounds of formula I are inhibitors of protein kinases such as the cyclin dependent kinases (cdks), for example, cdc2 (cdk1), cdk2, cdk3, cdk4, cdk5, cdk6, cdk7 and cdk8. The novel compounds of formula I are expected to be useful in the therapy of proliferative diseases such as cancer, inflammation, arthritis, Alzheimer""s disease and cardiovascular disease. These compounds may also be useful in the treatment of topical and systemic fungal infections.
More specifically, the compounds of formula I are useful in the treatment of a variety of cancers, including (but not limited to) the following:
carcinoma, including that of the bladder, breast, colon, kidney, liver, lung, ovary, pancreas, stomach, cervix, thyroid, prostate, and skin;
hematopoietic tumors of lymphoid lineage, including acute lymphocytic leukemia, B-cell lymphoma, and Burkett""s lymphoma;
hematopoietic tumors of myeloid lineage, including acute and chronic myelogenous leukemias and promyelocytic leukemia;
tumors of mesenchymal origin, including fibrosarcoma and rhabdomyosarcoma; and
other tumors, including melanoma, seminoma, teratocarcinoma, osteosarcoma, neuroblastoma and glioma.
Due to the key role of cdks in the regulation of cellular proliferation in general, inhibitors could act as reversible cytostatic agents which may be useful in the treatment of any disease process which features abnormal celluar proliferation, e.g., neuro-fibromatosis, atherosclerosis, pulmonary fibrosis, arthritis, psoriasis, glomerulonephritis, restenosis following angioplasty or vascular surgery, hypertrophic scar formation, inflammatory bowel disease, transplantation rejection, angiogenesis, and endotoxic shock.
Compounds of formula I may also be useful in the treatment of Alzheimer""s disease, as suggested by the recent finding that cdk5 is involved in the phosphorylation of tau protein (J. Biochem, 117, 741-749 (1995)).
Compounds of formula I may also act as inhibitors of other protein kinases, e.g., protein kinase C, her2, raf1, MEK1, MAP kinase, EGF receptor, PDGF receptor, IGF receptor, PI3 kinase, wee 1 kinase, Src, Ab1, VEGF, and 1ck, and thus be effective in the treatment of diseases associated with other protein kinases.
Compounds of formula I also induce or inhibit apoptosis, a physiological cell death process critical for normal development and homeostasis. Alterations of apoptotic pathways contribute to the pathogenesis of a variety of human diseases. Compounds of formula I, as modulators of apoptosis, will be useful in the treatment of a variety of human diseases with abberations in apoptosis including cancer (particularly, but not limited to, follicular lymphomas, carcinomas with p53 mutations, hormone dependent tumors of the breast, prostate and ovary, and precancerous lesions such as familial adenomatous polyposis), viral infections (including, but not limited to, herpesvirus, poxvirus, Epstein-Barr virus, Sindbis virus and adenovirus), autoimmune diseases (including, but not limited to, systemic lupus, erythematosus, immune mediated glomerulonephritis, rheumatoid arthritis, psoriasis, inflammatory bowel diseases, and autoimmune diabetes mellitus), neurodegenerative disorders (including, but not limited to, Alzheimer""s disease, AIDS-related dementia, Parkinson""s disease, amyotrophic lateral sclerosis, retinitis pigmentosa, spinal muscular atrophy and cerebellar degeneration), AIDS, myelodysplastic syndromes, aplastic anemia, ischemic injury associated myocardial infaretions, stroke and reperfusion injury, arrhythmia, atherosclerosis, toxin-induced or alcohol induced liver diseases, hematological diseases (including, but not limited to, chronic anemia and aplastic anemia), degenerative diseases of the musculoskeletal system (including, but not limited to, osteoporosis and arthritis), aspirin-sensitive rhinosinusitis, cystic fibrosis, multiple sclerosis, kidney diseases, and cancer pain.
In addition, the formula I compounds may be used for treating chemotherapy-induced alopecia, chemotherapy-induced thrombocytopenia, chemotherapy-induced leukopenia or mucocitis. In the treatment of chemotherapy-induced alopecia, the formula I compound is preferably topically applied in the form of a medicament such as a gel, solution, dispersion or paste.
The compounds of this invention may be used in combination with known anti-cancer treatments such as radiation therapy or with cytostatic and cytotoxic agents including, but not limited to, microtuble-stabilizing agents, microtuble-disruptor agents, alkylating agents, anti-metabolites, epidophyllotoxin, an antineoplastic enzyme, a topoisomerase inhibitor, procarbazine, mitoxantrone, platinum coordination complexes, biological response modifiers, growth inhibitors, hormonal/anti-hormonal therapeutic agents, haematopoietic growth factors, and the like.
Classes of anti-cancer agents which may be used in combination with the formula I compounds of this invention include, but are not limited to, the anthracycline family of drugs, the vinca drugs, the mitomycins, the bleomycins, the cytotoxic nucleosides, the taxanes, the epothilones, discodermolide, the pteridine family of drugs, diynenes, aromatase inhibitors, and the podophyllotoxins. Particluar members of those classes include, for example, paclitaxel, docetaxel, 7-O-methylthiomethylpaclitaxel (disclosed in U.S. Pat. No. 5,646,176), 3xe2x80x2-tert-butyl-3xe2x80x2-N-tert-butyloxycarbonyl-4-deacetyl-3xe2x80x2-dephenyl-3xe2x80x2-N-debenzoyl-4-O-methoxycarbonyl-paclitaxel (disclosed in U.S. Ser. No. 60/179,965) filed on Feb. 3, 2000 which is incorporated herein by reference thereto), C-4 methyl carbonate paclitaxel (disclosed in WO 94/14787), epothilone A, epothilone B, epothilone C, epothilone D, desoxyepothilone A, desoxyepothilone B, [1S-[1R*,3R*(E),7R*,10S*,11R*,12R*, 16S*]]-7,11-dihydroxy-8,8,10,12,16-pentamethyl-3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione (disclosed in WO 99/02514), [1S-[R*,3R*(E),7R*,10S*,11R*,12R*,16S*]]-3-[2-[2-(aminomethyl)-4-thiazolyl]-1-methylethenyl]-7,11-dihydroxy-8,8,10,12,16-pentamethyl-4,17-dioxabicyclo[14.1.0]heptadecane-5,9-dione (disclosed in U.S. Ser. No. 09/506,481 filed on Feb. 17, 2000 which is incorporated herein by reference thereto), doxorubicin, carminomycin, daunorubicin, aminopterin, methotrexate, methopterin, dichloro-methotrexate, mitomycin C, porfiromycin, 5-fluorouracil, 6-mercaptopurine, gemcitabine, cytosine arabinoside, podophyllotoxin or podophyllotoxin derivatives such as etoposide, etoposide phosphate or teniposide, melphalan, vinblastine, vincristine, leurosidine, vindesine, leurosine, and the like. Other useful anti-cancer agents which may be used in combination with the compounds of the present invention include, but are not limited to, estramustine, cisplatin, carboplatin, cyclophosphamide, bleomycin, tamoxifen, ifosamide, melphalan, hexamethyl melamine, thiotepa, cytarabin, idatrexate, trimetrexate, dacarbazine, L-asparaginase, camptothecin, CPT-11, topotecan, ara-C, bicalutamide, flutamide, leuprolide, pyridobenzoindole derivatives, interferons, interleukins, and the like. In addition, the compounds of this invention may be used in combination with inhibitors of famesyl protein transferase such as those described in U.S. Pat No. 6,011,029; anti-angiogenic agents such as angiostatin and endostatin; kinase inhibitors such as her2 specific antibodies; and modulators of p53 transactivation.
If formulated as a fixed dose, such combination products employ the compounds of this invention within the dosage range described below and the other pharmaceutically active agent within its approved dosage range. Compounds of formula I may be used sequentially, in any order, with known anti-cancer or cytotoxic agents when a combination formulation is inappropriate.
The present invention also provides pharmaceutical compositions which comprise a compound of this invention and a pharmaceutically acceptable carrier. It should be noted that, in the context of the pharmaceutical compositions of the present invention, the compounds of the invention, or compounds of formula I, refer to the free base, enantiomers, diastereomers as well as pharmaceutically acceptable salts. Examples of such pharmaceutically acceptable salts include, but are not limited to, hydrochloride, dihydrochloride, sulfate, trifluoroacetate, mixture of trifluoroacetate and hydrochloride, tartrate, fumarate, succinate, maleate, citrate, methanesulfonate, bromate and iodate salts. Also included are salts formed with other organic and inorganic acids such as hydroxymethane sulfonic acid, acetic acid, benzenesulfonic acid, toluenesulfonic acid and various others, e.g., nitrates, phosphates, borates, benzoates, ascorbates, salicylates, and the like. These salts include racemic forms as well as enantiomers and diastereomers (such as, for example, D-tartrate and L-tartrate salts). In addition, pharmaceutically acceptable salts of compounds of formula I may be formed with alkali metals such as sodium, potassium and lithium; alkaline earth metals such as calcium and magnesium; organic bases such as dicyclohexylamine, tributylamine, and pyridines, and the like; and amino acids such as arginine, lysine and the like.
The pharmaceutical compositions of the present invention may further comprise one or more pharmaceutically acceptable additional ingredient(s) such as alum, stabilizers, antimicrobial agents, buffers, coloring agents, flavoring agents, and the like. The compounds and compositions of this invention may be administered orally or parenterally including the intravenous, intramuscular, intraperitoneal, subcutaneous, rectal and topical routes of administration.
For oral use, the compounds and compositions of this invention may be administered, for example, in the form of tablets or capsules, or as solutions or suspensions. In the case of tablets for oral use, carriers which are commonly used include lactose and corn starch, and lubricating agents such as magnesium stearate are commonly added. For oral administration in capsule form, useful carriers include lactose and corn starch. When aqueous suspensions are used for oral administration, emulsifying and/or suspending agents are commonly added. In addition, sweetening and/or flavoring agents may be added to the oral compositions. For intramuscular, intraperitoneal, subcutaneous and intravenous use, sterile solutions of the active ingredient(s) are usually employed, and the pH of the solutions should be suitably adjusted and buffered. For intravenous use, the total concentration of the solute(s) should be controlled in order to render the preparation isotonic.
Daily dosages for human administration of the compounds of this invention will normally be determined by the prescribing physician with the dosages generally varying according to the age, weight, route of administration, and response of the individual patient, as well as the severity of the patient""s symptoms. A formula I compound of this invention is preferably administered to humans in an amount from about 0.001 mg/kg of body weight to about 100 mg/kg of body weight per day, more preferably from about 0.01 mg/kg of body weight to about 50 mg/kg of body weight per day, and most preferably from about 0.1 mg/kg of body weight to about 20 mg/kg of body weight per day.
cdc2/cyclin B 1 kinase activity was determined by monitoring the incorporation of 32P into histone HI. The reaction consisted of 50 ng baculovirus expressed GST-cdc2, 75 ng baculovirus expressed GST-cyclin B1, 1 xcexcg histone HI (Boehringer Mannheim), 0.2 xcexcCi of 32P xcex3-ATP and 25 xcexcM ATP in kinase buffer (50 mM Tris, pH 8.0, 10 mM MgCl2, 1 mM EGTA, 0.5 mM DTT). The reaction was incubated at 30xc2x0 C. for 30 minutes and then stopped by the addition of cold trichloroacetic acid (TCA) to a final concentration of 15% and incubated on ice for 20 minutes. The reaction was harvested onto GF/C unifilter plates (Packard) using a Packard Filtermate Universal harvester, and the filters were counted on a Packard TopCount 96-well liquid scintillation counter (Marshak, D. R., Vanderberg, M. T., Bae, Y. S., Yu, I. J., J. of Cellular Biochemistry, 45, 391-400 (1991), incorporated by reference herein).
cdk2/cyclin E kinase activity was determined by monitoring the incorporation of 32P into the retinoblastoma protein. The reaction consisted of 2.5 ng baculovirus expressed GST-cdk2/cyclin E, 500 ng bacterially produced GST-retinoblastoma protein (aa 776-928), 0.2 ,xcexcCi 32P xcex3-ATP and 25 xcexcM ATP in kinase buffer (50 mM Hepes, pH 8.0, 10 mM MgCl2, 5 mM EGTA, 2 mM DTT). The reaction was incubated at 30xc2x0 C. for 30 minutes and then stopped by the addition of cold trichloroacetic acid (TCA) to a final concentration of 15% and incubated on ice for 20 minutes. The reaction was harvested onto GF/C unifilter plates (Packard) using a Packard Filtermate Universal harvester, and the filters were counted on a Packard TopCount 96-well liquid scintillation counter.
cdk4/cyclin Dl kinase activity was determined by monitoring the incorporation of 32P in to the retinoblastoma protein. The reaction consisted of 165 ng baculovirus expressed as GST-cdk4, 282 ng bacterially expressed as S-tag cyclin D1, 500 ng bacterially produced GST-retinoblastoma protein (aa 776-928), 0.2 xcexcCi 32P xcex3-ATP and 25 xcexcM ATP in kinase buffer (50 mM Hepes, pH 8.0, 10 mM MgCl2, 5 mM EGTA, 2 mM DTT). The reaction was incubated at 30xc2x0 C. for 1 hour and then stopped by the addition of cold trichloroacetic acid (TCA) to a final concentration of 15% and incubated on ice for 20 minutes. The reaction was harvested onto GF/C unifilter plates (Packard) using a Packard Filtermate Universal harvester, and the filters were counted on a Packard TopCount 96-well liquid scintillation counter (Coleman, K. G., Wautlet, B. S., Morissey, D, Mulheron, J. G., Sedman, S., Brinkley, P., Price, S., Webster, K. R. (1997) Identification of CDK4 Sequences involved in cyclin D, and p16 binding. J. Biol Chem. 272,30:18869-18874, incorporated by reference herein).